From the SAM website:
SAM is a program to monitor (in real-time) the number of alerts generated by Snort. Having recently set up Snort and ACID I felt like there was something missing.

Snort was great for identifying suspicious traffic and ACID was great for digging in to the details but I needed something that was a little higher overview and able to sounds alarms if certain conditions were met.

For instance if I was attacked 100 times in a 5 minutes period. SAM does not replace Snort or ACID but rather it compliments them.

Where can I get SAM and SNORT?:
SAM - http://freesoftware.lookandfeel.com/sam/
SNORT - http://www.snort.org/